During the First World War both the United Kingdom and Germany attempted to carry out naval blockades of the other.

Blockades had been a part of British strategy in its wars with European enemies for many years. In the early 18th century they were mainly strategic, with the intention of giving warning if enemy fleets came out of port. By the end of that century, they also aimed at damaging enemy trade.

The UK had paid little attention to the rights of neutrals during its 18th and early 19th century wars: this was one of the causes of the War of 1812 with the United States of America. In 1856, however, it signed the Declaration of Paris, which stated that belligerents should not interfere with neutral trade. including enemy cargoes carried in neutral ships and neutral cargoes carried in enemy ships.

However, the protection offered to neutral trade did not extend to contraband, which was divided into two categories. Absolute contraband was items useful only to the military. Conditional contraband meant goods with both peaceful and military uses that were clearly destined for the enemy’s armed forces.

Conditional contraband was not defined by the Declaration of Paris. The UK insisted that it did not include food, but other countries disagreed. France, supported by Germany, declared it to be contraband during its 1885 war with China, as did Russia in the 1904-5 Russo-Japanese War.

The UK was the world’s largest shipping carrier, a net importer of food and an exporter of manufactured goods. It had to consider the issue from three viewpoints: as a neutral in other people’s wars; the defensive one of defending its own trade; and the offensive one of blockading the enemy. Defensively, in a war with another country, it could continue to import from the USA in US ships. However, other European countries were less vulnerable to blockade than they had been before the development of railways, provided that they neighboured neutral countries.

In 1909 the Declaration of London attempted to define contraband. Absolute contraband was confined to a small number of purely military items, whilst the list of supplies defined as conditional contraband included food provided that it was for military, not civilian consumption.

The British delegates agreed the terms of the Declaration of London, but the UK never ratified it. There were protests from the public, which focussed mainly on the neutral and defensive angles, and a petition signed by 138 retired admirals.

Sir Edward Grey, the Foreign Secretary, and the Foreign Office accepted the Declaration. They were concerned mainly with the neutral and defensive issues of protecting Britain’s merchant fleet and its wartime food supply.[1]

The Admiralty was planning to conduct economic warfare in the event of a war with Germany, which makes the agreement of its delegates to the London Conference more puzzling. Avner Offer suggests that it may have been ‘partly a matter of muddle and neglect’, but also offer a ‘more Machiavellian interpretation’; Admiral Lord Fisher, the First Sea Lord, may have wanted the UK to have legal protection when a neutral, but expected it to act in its self interests in wartime.[2]

Some contemporary writers, such as Thomas Gibson Bowles, feared that the 1909 Declaration of London would prevent the Royal Navy from exerting the same pressure on a future enemy that they claimed had won past wars. However, Archibald Bell, the Official Historian of the British blockade, argues that Bowles’s claim that past blockades had been decisive was wrong. Bell contends that British leaders of the past ‘had never hoped that a continental enemy could be brought to terms by stopping its commerce.’[3]

Fisher’s immediate successor as First Sea Lord, Admiral Sir Arthur Wilson, was sceptical about the merits of blockade, but he had retired by 1914. By then British strategy was to blockade Germany in wartime. The UK was allied to France and Russia, so the fears that a naval blockade would be circumvented by trade with neighbouring countries no longer applied. Germany was surrounded and her trade with the rest of the world could be stopped if Antwerp and Rotterdam were blockaded.[4]

Just before the start of the war the British decided that the traditional policy of a close blockade of enemy ports was no longer viable because of the threat of attack from torpedo armed enemy vessels on the blockading force. Instead, a distant blockade would be carried out. The Channel Fleet would block the English Channel, whilst a line of cruisers from the Shetland Islands to Norway would close the northern entrance to the North Sea.

There were, however, some difficulties in implementing the blockade when war came. One was the doctrine of continuous voyage. Absolute contraband intended for Germany could be stopped even if it was to be first unloaded in a neutral port such as Rotterdam and then transported by land to Germany. However, the Declaration of London stated that conditional contraband could only be stopped if it was heading directly to an enemy port.

The UK was reluctant to abandon entirely the Declaration of London, partly because Grey did not want to give up his support for neutral rights and international law and partly because it did not want to offend the USA.

However, the Germans laid unanchored, floating mines in the North Sea early in the war. International law said that such mines had to become inoperable after an hour. It was not feasible to do so, but this gave the UK an opportunity to argue that it was Germany that had first broken international law. The UK then announced that it would apply continuous voyage to conditional as well as to absolute contraband.

The UK also decided the treat food as contraband after it received reports that all food distribution in Germany was to be taken over by the government. The reports were actually an exaggeration of a plan to control food prices, but the British went ahead. However, the early British efforts at blockade did not have the desired effect. There was a reluctance to take measures that would offend neutrals who also supplied the UK.[5]

The naval force carrying out the blockade was also weak. Eric Osborne describes Rear Admiral Dudley De Chair as ‘an excellent choice for the job’ of commanding the 10th Cruiser Squadron, responsible for closing the northern approaches to the North Sea.[6] However, he initially had only six Edgar and two Royal Arthur class cruisers, launched in 1890-92. They were too slow to catch blockade runners and struggled in the harsh weather of their patrol area. they also had to take part in sweeps of the North Sea by the Grand Fleet. On 15 October one of them, HMS Hawke, was sunk by U9.

On 5 November the Admiralty announced that the whole of the North Sea was a war zone, warning that ships entering from the north would do so at their own risk. The official reason for this was the German minefields, but the real one was to force neutral ships heading into the North Sea to go through the English Channel, making it easier to search them for contraband. A number of Scandinavian shipping companies agreed that their ships would call at Kirkwall for inspection in return for being allowed to use the northern route.

The blockade was also strengthened in December by the replacement of the 10th Cruiser Squadron’s old ships with 23 armed merchant cruisers, merchant liners requisitioned by the navy and armed. They were both more numerous and more suitable for their role than the old warships initially assigned to it.[7]

The British blockade was not as successful in 1914 as its planners had hoped. It later tightened because the UK signed agreements with neutral countries, but only one of these, with the Netherlands on 23 November, was concluded in 1914. The UK had to move slowly because it could not afford to offend neutrals, especially the USA.[8]

The greatest British success in destroying German trade in 1914 was in sweeping the German merchant fleet from the seas, causing major economic problems for Germany. In November there were 221 German merchant ships were laid up in German ports and 1,059 in neutral ports, with another 245 having been interned in Allied ports.[9]

Osborne argues that:

‘The official reports on Germany’s economic conditions for November and December revealed hardship, but not sufficient to cripple the German war effort…The greatest achievement of British negotiations in 1914 was not the practical results achieved but the establishment of a foundation for future tightening of the blockade…The deadlock on the Western Front meant that economic pressure was vital to the success of the Allied cause and measures to date were not satisfactory.’[10]

The development of the British blockade was an example of the way in which a breach of international law by one side would be used by the other to justify a further breach, leading towards total war. The next escalation would be made by the Germans, when they used the British declaration that the North Sea was a war zone to justify the implementation of unrestricted submarine warfare.